The effect of magnification on sonographically measured nerve cross-sectional area.

Introduction: The primary aim of this investigation was to determine whether use of write-zoom magnification affects sonographically determined cross-sectional area (CSA) of peripheral nerves.

Methods: CSAs of the median (MN) and posterior interosseous (PIN) nerves were measured in 22 limbs from 11 asymptomatic volunteers using both standard imaging and write-zoom magnification. CSA measurements were repeated on the same images 1 week later.

Results: The average CSA of write-zoomed images for the MN was significantly larger at both measurement sessions (week 1: 11.1 mm(2) write-zoom vs. 10.0 mm(2) standard, P = 0.019; week 2: 11.8 mm(2) vs. 10.4 mm(2), P = 0.023). Similar differences were noted for the PIN (week 1: 2.3 mm(2) vs. 1.9 mm(2), P = 0.002; week 2: 2.5 mm(2) vs. 1.9 mm(2), P = 0.001).

Conclusions: Write-zoom magnification may significantly increase the measured CSA of peripheral nerves. These changes appear to be more substantial when smaller nerves are measured.